A prosthetic device is an artificial device used to replace a body part. For example, since the 1960's, prosthetic devices have been used in hip replacement surgery. Hip replacement surgery is an increasingly common surgery used to treat joint failure in patients. Joint failures are often caused by diseases such as osteoarthritis, rheumatoid arthritis etc. Treating joint failures by hip replacement typically involves replacing the ball on the femur (the bone that extends from the pelvis to the knee) with a prosthetic ball and replacing the socket in the hip with a prosthetic socket. The socket is part of the pelvis and the ball fits into the socket.
Though medical practitioners have been performing hip replacement surgeries for more than half a century, at least two significant problems persist with this medical procedure. First, the prosthetic ball sometimes dislocates from the prosthetic socket (i.e., the prosthetic ball comes out of the prosthetic socket). Improper alignment of the prosthetic ball and socket during hip replacement surgery is one factor that causes dislocation of the prosthetic ball from the prosthetic socket after surgery. Second, depending to some extent on the materials used to make the prosthetic ball and socket, excessive wear of those materials may occur as the prosthetic ball moves in the prosthetic socket during use. As with the dislocation problems, improper alignment of the ball and socket during surgery is one major factor that causes excessive wear during use. For example, excessive wear occurs when the prosthetic ball rubs excessively on one edge of the socket. This is known as edge loading. Wear debris, such as formed by edge loading in the joint, can cause major complications such as inflammation and loosening of the prosthetic components. Moreover, when the prosthetic components wear out or loosen, they have to be replaced in another hip replacement surgery.
Because of the problems associated with improperly aligned prosthetic sockets and balls, medical practitioners generally make every effort to try and properly align these devices during surgery. Most medical practitioners rely on their experience to view the bone cavity and manually place the prosthetic socket in the proper position. For example, the proper alignment of the hemispherical socket in the acetabula (the cup-shaped cavity in the pelvis into which the ball-shaped head of the femur fits) is typically attained when it is about 40° to 45° of abduction. Additionally, when the prosthetic socket is properly aligned in the acetabula, the open area of the socket typically should be about 10° to 20° of anteversion, i.e., facing forward. It should be noted that though the abduction angle is typically about 40° to 45° and the anteversion angle is typically about 10° to 20°, variations outside these ranges are possible and the embodiments of the invention disclosed herein may be used in instances outside of the typical ranges.
Particularly because medical practitioners are now doing surgeries with smaller incisions than have traditionally been used, it is not uncommon that manual fitting of a prosthetic socket during hip surgery results in the prosthetic socket being placed at an angle of 50° to 60° and even facing slightly backward (retroversion). Such improper alignment generally results in dislocations of the hip and excessive wear of the prosthetic ball and socket after surgery. To improve upon manual alignment of prosthetic sockets, medical practitioners have tried to use positioning devices based on x-ray, fluoroscopy, MRI and other electronic technology. Despite these technologies, improper alignments of prosthetic balls and sockets persist and these improper alignments in turn cause complications such as dislocations and excessive wear. Moreover, apart from the limited success with the current positioning devices, these devices are expensive to make and operate.